Cannot add user in Jira group. User is already a member of the "group"

We have an issue on specific user. There is no notification was being emailed to him even he is a member of the said group. Base on the investigation user he is not member of the group however even we added to the group it said the user is already a member. There are a lot of associated projects Is there a way how to fix the group without deleting the group and recreate again.

If you spend enough time as a Jira admin - whether you are managing a single, mid-sized instance, a large enterprise one or juggling multiple instances at once - you will eventually find yourself in ...